Film blowing orientation studies

The film-blowing process is used industrially to manufacture plastic films that are biaxially oriented. Many attempts have been made to predict and model this complex but important process, which continues to mystify rheologists and polymer processing engineers worldwide. A constitutive equation, able to predict well the polymer melt in all forms of deformation, is required to model the process, together with the standard conservation equations of continuity, momentum, and energy. Pearson and Petrie [125,126] were the first to predict the forces within the blown film by the use of the thin-shell approximation, force balances, and the Newtonian constitutive equation. The use of the thin-shell approximation and force balances is standard in any attempt to model the film-blowing process, and it has been used in the vast majority of subsequent studies. 

As noted, each polymer has a temperature at which the heated preform or parison should be stretch blow-molded to achieve maximum orientation properties. Each polymer exhibits its own natural stretch ratio. Orientation of polymers is a study by itself, and there are references to in-depth study of specific polymers (13) (see also. Films, Orientation). 

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